An Examination of the Assumption That the Equating of Parallel Forms Is Population‐independent

Linear conversions were developed relating scores on two recent forms of the homogeneous GRE Quantitative Test (GRE‐Q) and the specially constituted heterogeneous GRE Verbal‐plus‐Quantitative Test (GRE‐V+Q), using randomly equivalent groups of about 13, 000 taking each form. Specially defined homogeneous subpopulations were then identified, and conversions between scores on the two forms were again calculated, this time based on l000‐case samples drawn at random from the subpopulations. Finally, in order to develop empirical measures of equating error, I00 samples of 1, 000 cases each were drawn at random from the two total groups and used to calculate 100 conversions between scores on the two forms. The conversions based on the specially selected subpopulations were then compared with the total‐group conversions and evaluated in terms of the empirical standard errors. The results showed that the conversions for the subpopulations agreed with the total‐group conversion quite satisfactorily for the GRE‐Q and almost as well for the GRE‐V+Q. It was concluded that the data clearly support the assumption of population independence for homogeneous tests, but not quite so clearly for heterogeneous tests.